- Wait a day after you have caught the trio and make sure it is day.
- Have the trio in your party
- Talk to the girl in Pacifidlog again
Hopefully this works, I've searched a bit and some people said they couldn't get it until a day after. Some others said that they were only able to get it when it was day.
Source, Othersource and various comments made by people on other sites
If you are having trouble finding the actual thing, look here (sorry for non-ORAS pic, I had to photoshop it myself and I couldn't find an ORAS one)
And remember, the actual island is at Route 105.